Lets say i have an item 'odc' which has no buyer code in seattle organization (m1 organization code). I want to update and asscoiate 'west, rod' as buyer
To the item 'odc'.
First check under setup > items > attribute contol to check if it controlled at the organization level or master level. In our case the attribute is controlled at the org level.
Now we check if rod exists in the list of valid buyers.

INSERT INTO mtl_system_items_interface (process_flag,
set_process_id,
transaction_type,
organization_id,
Inventory_item_id,
buyer_id)
VALUES (1,
1,
'update',
2828,
6891,
57);Commit;
Now you will observe that the transaction type is 'update' because we are updating an existing record. I am also using inventory_item_id because when you use id's the performance is better. And also when running the item import i use value 2 in create or update items field.

Now run the item import program ie. Item > import > import items.
In process set enter 1 as we had used 1 in the set_process_id column. Now enter 2 in create or update items field and hit ok button.

You can check view requests to check whether your request has completed
Successfully.now go to organization items and query on 'odc' item in m1 organization. Under purchasing tab you will see that the buyer 'west, rod' populated.

Importing master and child records
==================================
Previously, ioi processed items in an order that did not recognize that master
Items were loaded before child records in mtl_system_items. Therefore, users
Were advised to import master records first in one run and then separately
Import child records.
The
code now automatically separates master records from children, and
Processes master records first. However, as one ioi process is not aware of
Other ioi processes running in parallel, do not split a given item's separate
Organization records into two different set_process_ids that are being run in
Parallel. Doing so may cause the child record to be processed before the
Master record.

Master level controlled attributes are correctly propagated to the child
Records when the master item record is updated.
When launching items into the master item org, the child records are copied
Into mtl_system_items_interface for validation, and are identified with a
Transaction_type of 'auto_child'.

Note:if you are importing master and child records, insert them into the
Mtl_system_items_interface and mtl_item_revisions_interface tables, and run
Them at the same time by setting the 'all organizations' parameter to 'yes'.
If you do not do this, then the child revision records will not be imported.

Error checking:
======================================
When importing multiple revisions, if one record for an item fails validation, all revisions for that item fail.